package bstsetcode.linkedlistqueue;


/**
 * 链表实现队列--没有使用虚拟头结点
 * 因为我们不需要操作中间的元素，所以不使用虚拟头结点
 * @author noob
 * @version 1.0
 * @date 2021/3/15 9:58
 */
public class LinkedListQueue<E>  implements Queue<E> {

    private class Node{
        E e;
        Node next;

        public Node(E e, Node next) {
            this.e = e;
            this.next = next;
        }

        public Node(E e){
            this(e,null);
        }

        public Node() {
            this(null,null);
        }

        @Override
        public String toString() {
            return e.toString();
        }
    }

    private Node head,tail;
    private int size;

    public LinkedListQueue(){
        head = null;
        tail = null;
        size = 0;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    @Override
    public void enqueue(E e) {
        if(tail == null){
            tail = new Node(e);
            head = tail;
        }else {
            tail.next = new Node(e);
            tail = tail.next;
        }
        size++;

    }

    /**
     * 如果head为null，tail也要为null；
     * @return
     */
    @Override
    public E dequeue() {
        if(isEmpty()){
            throw  new IllegalArgumentException("队列为null，不能出队");
        }
        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if(head == null){
            tail = null;
        }
        size--;

        return retNode.e;
    }



    @Override
    public E getFront() {
        if(isEmpty()){
            throw  new IllegalArgumentException("队列为null");
        }
        return head.e;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append("LinkedListQueue: front ");

        Node cur = head;
        while(cur != null) {
            res.append(cur + "->");
            cur = cur.next;
        }
        res.append("NULL tail");
        return res.toString();
    }

    public static void main(String[] args) {
        LinkedListQueue<Integer> queue = new LinkedListQueue<>();
        for(int i = 0 ; i < 10 ; i ++){
            queue.enqueue(i);
            System.out.println(queue);

            if(i % 3 == 2){
                queue.dequeue();
                System.out.println(queue);
            }
        }
    }


}
